What are the most efficient workflows to create all quad junctions?
The easiest way that comes to mind currently is to remove  the critical faces, add some loop cuts, then create faces.  

So for the second one, you would remove the critical face,
make a double loop cut with Ctrl R
then 2 then extrude the small edge in the middle,
and finally select the edge pairs to Fill them with F.

The same applies to the third and fourth with some changes. For
the first one: Remove the upper two critical faces, add the loop
cuts, fill the proper edge pairs, move the center vertex down.